Control system for regulating flow of molten metal into a continuously rotated casting wheel



United States Patent Office 3,528,479 Patented Sept. 15,, 1970 CONTROL SYSTEM FOR REGULATING FLOW F MOLTEN METAL INTO A CONTINUOUSLY ROTATED CASTING WHEEL Joseph I. Cole, Staten Island, N.Y., and William C. Martin, Naperville, and Stephen F. Skala, Berwyn, Ill., assignors to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed July 7, 1967, Ser. No. 651,871 Int. Cl. B22d 11/10 US. Cl. 164155 7 Claims ABSTRACT OF THE DISCLOSURE A tapered metering pin in a nozzle controls the flow of molten metal from a tundish into a casting groove in a continuously rotated wheel. A gamma radiation source and a detector are positioned at opposite sides of the wheel to monitor both the quantity of metal flowing into the casting groove and the level of metal in the groove. A control system positions the metering pin in response to total radiation detected so as to maintain the flow and the level substantially constant.

BACKGROUND OF THE INVENTION In the continuous casting of molten metal, it is known to continuously supply molten metal, such as copper, from a tundish into a mold. For example, the molten metal may be gravity fed into a peripheral groove in a continuously rotated casting wheel. The wheel is rotated at essentially a constant speed. A traveling band contacts an arcuate portion of the periphery of the wheel to enclose a sector of the groove. The band travels in contact with the wheel at a velocity equal to the tangential velocity of the wheel. The molten metal moves with the rotating wheel and the traveling band through the enclosed sector and is cooled to solidify therein. The essentially constant speed of Wheel rotation permits uniform solidification of the metal in the groove, since the solidifying metal is essentially free of tangential forces caused by acceleration or deceleration and is retained and cooled in the groove for a uniform time period. A solid metal bar is removed from the groove after the traveling band parts from the periphery of the wheel.

In order to obtain a sound and uniform casting, it is necessary that the passage of molten metal from the tundish into the casting wheel groove be Continuously maintained substantially at a predetermined flow rate. This predetermined flow rate is coordinated with the constant speed of rotation of the casting wheel to continuously provide a predetermined quantity of metal within the groove. Inexact control may also cause overflow of molten metal which results in the formation of fins on the cast bar. Such fins can damage the rolls of a mill for rolling the continuously cast bar into rod and can cause defects in the resulting rod.

Flow control is complicated by occasional variations in the depth of molten metal in the wheel-feeding tundish and by changes in viscosity of the molten metal. Manual control by an operator visually observing the level of molten metal in the casting groove and rnanipulating a flow regulating mechanism to maintain this level approximately constant provides an inexact and unreliable manner of flow control, subject to human delays in carrying out corrective operations and largely de* pendent upon the skill and alertness of the. operator. Thus, it is desirable to provide a direct and reliable automatic flow control system which will rapidly function to eliminate any variations in the rate of flow of molten metal between a tundish and a continuous casting mold.

Typical known automatic control systems for regulating the flow of molten metal into a continuous casting mold involve controlling the initial introduction of molten metal into the tundish so as to regulate indirectly the flow from the tundish into the 'mold. This manner of indirect control is not always sufficiently accurate. These and other systems generally depend upon a continuous monitoring of the metal level within the mold. The monitoring may involve the use of thermocouples, an impractical expedient where the mold is a continuously rotating, grooved wheel. The aforementioned systems detect changes in the level of molten metal within the mold. Corrections for controlling the flow rate from the tundish to the mold are made in response to changes in the metal level. Such systems are subject to a built-in delay in performing the corrective operations. Flow control systems of this type must await the entry of the flowing metal into the mold :before the effect of a varying flow rate can be felt in variations in the monitored level. Only thereafter can corrective action be initiated. Due to the delayed response of the control system to variations in the flow rate of molten metal, the system attempts to correct a previous condition which may no longer be existent or may have become aggravated. Undue inaccuracy in control and undesirable overshooting of the proper corrective position of the flow regulating apparatus may result. In order to avoid such delays in control, it is desirable to provide for the automatic metering of the flow of molten metal between a tundish and a continuous casting mold based not only upon measurements of the level of molten metal in the mold, but also upon direct measurements of the quantity of molten metal flowing between the tundish and the mold, variations therein being indicative of the rate of an impending change in the level of metal within the mold.

SUMMARY THE INVENTION An object of the invention resides in a new and improved control system for regulating the flow rate of molten metal traveling from a tundish into a casting groove in a continuously rotated casting wheel.

In accordance with the invention, a nozzle directs molten metal, such as copper, to flow from an orifice at the bottom of a tundish into a casting wheel groove. An incrementally adjustable flow metering pin or valve is positioned in the nozzle to precisely regulate the flow of the molten metal. In flowing between the tundish and the groove, the molten metal passes through an entrance zone adjacent the groove. A source of gamma radiation is positioned at one side of the casting wheel and a gamma radiation detecting device is positioned at an opposite side thereof. These are so located that radiation from the source impinging on the detecting device must travel across a V-shaped gap which follows the curvature of the casting groove and which includes both the entrance zone and a portion of the groove receiving the flowing metal. Greater or lesser inhibition of gamma radiation transmittal, reflecting the presence of greater or lesser amounts of all of the molten metal in this gap between the source and the detector, is sensed. A correction signal is generated whenever the level of radiation detected varies from a predetermined value. The correction signal is proportional to the deviation of the radiation level from the predetermined standard, which corresponds to both a desired quantity of molten metal flowing through the gap and a desired level or height of metal in the casting groove. A control mechanism precisely positions the metering pin in response to the amplitude of the generated correction signal to readjust the flow to the desired rate.

3 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is an isomeric view of an apparatus for the continuous casting of molten metal, showing a grooved continuous casting wheel fed by molten metal flowing from a tundish and illustrating, partly in block diagram form, a control system for metering the flow of molten metal from the tundish to maintain a predetermined flow rate and a predetermined level of molten metal in the casting wheel groove in accordance with the principles of the invention; and

FIG. 2 is a side elevational view of a portion of the apparatus, showing part of a flow directing tundish outlet nozzle and a V-shaped field or area through which both the quantity of metal flowing from the nozzle and the level of metal in the groove are monitored by a detecting mechanism forming a part of the control system.

DETAILED DESCRIPTION Referring now to FIG. 1 of the drawing, there is illustrated an apparatus for continuously casting molten metal, such as copper. This apparatus includes a casting wheel 11, having a casting groove 12 therein for receiving molten metal, which is mounted for rotation on a shaft 13. The shaft 13 is continuously rotated, to rotate the wheel 11 at a constant speed in the direction of the arrow, by a motor and drive train (not shown) during the continuous casting of molten metal. A traveling continuous band 14 contacts the periphery of the casting wheel for an arc of the order of 180 degrees of the wheel. The band defines with the groove 12 a closed channel or chamber, traveling with the rotating wheel, for containing molten metal. The band 14 extends between the casting wheel 11 and an idler wheel 16 and is driven by or with the rotation of the casting wheel to continuously maintain slip-free contact with the periphery thereof.

A tundish 17 has a tapered outlet orifice 18 through 'its side or bottom surface. An outlet nozzle 19 depends from the tundish and surrounds the orifice 18. The nozzle is positioned to introduce a stream of molten metal 21, such as copper, by gravity feed from the tundish 17 into the closed channel or chamber between the band 14 and the edges of the casting groove 12. The molten metal enters this channel at an entrance point or receiving mouth 22 slightly below the position at which the band first contacts the periphery of the casting wheel. The outlet nozzle 19 is in the form of a funnel or spout into which a tapered flow metering pin or valve 23 projects from within the tundish 17. The metering pin is preferably composed of stainless steel. The tapered internal surface of the nozzle 19 and the taper on the metering pin 23 are interrelated so that incremental differences in flow are effected by small axial movements of the metering pin in either direction within the nozzle.

Molten metal entering the casting groove 12 in the rotating casting wheel at the entrance point or receiving mouth 22 is transported in the moving, closed channel or chamber between the edges of the groove and the moving band 14. The metal leaves the wheel at an exit point 24, spaced by a distance of the order of 180 degrees about the periphery of the casting wheel from the entrance point 22. Located adjacent the closed channel between the points 22 and 24 is a heat exchange apparatus, such as a. group of water-spraying nozzles (not shown), for cooling the molten metal. The heat exchange apparatus may be positioned adjacent the band 14 and adjacent and/or within the casting wheel 11. Due to the cooling of the molten metal within the casting groove 12, the casting wheel 11 and the band 14 cooperate to In order that the cast bar 26 be continuously produced by the apparatus, it is necessary that a continuous supply of molten metal be gravity-fed from the tundish 17 to the casting wheel 11. A necessity for uniformity of the product requires that the casting wheel 11 be rotated at constant speed and that the flow rate of molten metal into the casting groove 12 adjacent the entrance point 22 be kept substantially constant. A continuously constant quantity of metal is thereby maintained in the groove. A control system used with the apparatus provides for corrective repositioning of the tapered metering pin 23 in the tundish nozzle or spout 19 whenever the fiow rate of molten metal, manifested as a motion of the molten metal toward the casting groove, varies from a predetermined value or whenever the height of metal in the groove varies from a predetermined level.

The level of molten metal in the wheel-feeding tundish 17 may be continually replenished from a spout 27 of a tiltable holding furnace under the regulation of a suitable control system for maintaining the tundish level substantially uniform. The tundish-to-wheel flow control system employing the tapered metering pin 23 will rapidly compensate for any uncontrolled fluctuations in the level of the molten metal in the tundish, as well as for variations in the viscosity of the molten metal in the tundish. Thus, overflow of molten metal from the casting groove 12 is prevented, as is underfilling which reduces cooling action, while the continuous production of uniform, high quality bar, suitable for rolling into rod and drawing into wire, is assured.

The system for controlling the flow of molten metal into the entry mouth 22 includes a source 31 of gamma radiation, for example (FIG. 2) millicuries of cesium 137 fused into each of two stainless steel rods 31' of /2 inch diameter and 8 /2 inch length. The radiation source 31 extends generally vertically along one side of the casting wheel 11 adjacent the entrance point 22 at the periphery of the wheel. The source is shaped to provide a substantially linear signal corresponding to the level of cast metal in the wheel 11. The radioactive rods 31' are preferably mounted to form a V so that at all points along the measured interval, radiation passes through a major diagonal of the cast bar into a gamma radiation detector 32 on the opposite side of the wheel. The V shape substantially conforms to the segment of the groove 12 which is to be monitored. Lead shielding (not shown) preferably surrounds all surfaces of the source with a movable lead shutter arranged to expose that surface facing the casting wheel 11.

The gamma radiation detector 32, for example a cylinder 10 inches long by 1 inch in diameter, is positioned at the opposite side of the periphery of the casting wheel from the source 31 and is also adjacent the entrance point 22. The gamma radiation detector may consist of a thallium activated sodium iodide crystal 33 serving as a primary detector and an internal calibration system containing an americium 241 source as a standard. The detector is coupled to a photomultiplier and a preamplifier 34, located with the detector in a steel housing.

A high voltage power supply 36 is connected to operate the detector 32. An electronic stabilizer 37 serves to lock onto the alpha pulses of the americium 24l source within the detector 32 and to vary the high voltage so that the alpha pulses at the amplifier output are of constant magnitude. Pulses which correspond to the 5.5 mev. americium 241 alpha particle are easily separable from those of the 0.661 mev. gamma particle. The stabilizer 37 is coupled to the power supply 36 and to an amplifier 38 coupled to the output of the preamplifier 34. The stabilizer compensates for drift in the high voltage power supply 36, in the amplifiers 34 and 38, and in the conversion efliciency of the detector and photomultiplier.

Turning to FIG. 2, the zone formed by an overlap between the radioactive rods 31' and the detector 32 constitutes the area or field of operation of the detector 32, i.e., the gap through which the transmittal of radiation may be detected. This detection zone includes a portion of the groove 12 surrounding the entrance point 22. The generally V-shaped field or gap constituting this detection zone between the source and the detector also includes an upwardly extending area through which the molten metal flows between the nozzle 19 and the entrance point 22. This area forms an entrance zone 39 adjacent the entrance point through which all molten metal entering the groove 12 must first flow. In summary, the cross-sectional area of the gamma radiation detection zone follows generally the curvature of the casting wheel and is of such size as to encompass the entry mouth 22, the flowing stream 21 of molten metal in the entrance zone 39, and a portion of the metal beneath the surface level in the casting chamber. The described V shape is well suited to monitor the curving groove 12 and a portion of the entrance zone 39 to be monitored.

The presence of molten metal in the gap or detection zone between the gamma radiation source 31 and the detector 32 is reflected in the total radiation transmitted through the gap. The molten metal inhibits gamma radiation transmittal, so that a lesser radiation sensed by the detector indicates a greater quantity of metal within the gap and a greater total radiation sensed by the detector indicates a lesser quantity of metal within the gap.

Since the gap or field includes both the upwardly extending entrance zone 39 and a portion of the groove 12 beneath the entrance point 22, the instantaneous total of transmitted gamma radiation provides a measurement both of the quantity of molten metal flowing between the tundish 17 and the groove 12 and of the instantaneous height or surface level of molten metal within the groove 12. The height of molten metal in the groove serves as an indicator of the quantity of molten metal instantaneously being cast on the grooved wheel 11, while changes in the quantity of molten metal flowing through the entrance zone 39 foreshadow any impending change in the level of metal in the wheel groove =12. Both quantities of metal must be maintained substantially free from variation in order to assure production of uniform rod suitable for rolling and drawing into wire.

Considering now the operation of the apparatus, assume first a steady-state condition in which the tapered flow metering pin 23 (FIG. 1) is maintained stationary in the nozzle 19. A predetermined, constant flow rate of molten metal through the entrance zone 39 maintains a desired amount of metal in the casting wheel groove 12. The level of gamma radiation transmitted through the V-shaped field or gap (FIG. 2) is sensed by the detector 32. The scintillation crystal 33 emits low level light energy which is converted to an electrical signal by the photo-multiplier tube. This signal, indicative of the level of transmitted radiation, is fed to the preamplifier 34. The signal is at a predetermined level, corresponding to the amount of molten metal in the detection zone being at a desired value. The signal is amplified by the amplifier 38 and is fed to a conventional discriminator 40. The discriminator 40 responds to all scintillation pulses above a preset discriminator level. The output pulses of the discriminator 40 are filtered by a rate circuit 41 to provide a first voltage signal 62 which varies directly with respect to the count rate. A differentiating circuit 61 preferably also differentiates the first signal to a second voltage signal 62 proportional to the rate of change of the level of molten metal in the groove 12 and therefore indicative of the flow rate. The voltage signals 62 and 63 are applied to a conventional indicating controller 42 which acts to convert the combined electrical signal into a pneumatic control signal. A supply line 43 is connected to a source of pressurized air, e.g., at up to 20 p.s.i.g. The supply line deli-vers this pressurized air to the controller 42, which meters the flow of the pressurized air out through the fluid line 44 in accordance with the voltage of the input signal.

Pressurized air, regulated by the controller 42, is fed through the fluid line '44 to a diaphragm 45 for positioning a conventional pneumatic pilot valve 46 having a pair of pistons 50. The pilot valve regulates the application of pressurized air from a supply line 47 to alternate sides of an actuating piston 48 in a cylinder 49. The pressurized air entering through the supply line 47 is at suitably high pressure, e.g., 60 p.s.i.g., for positioning the piston 48 in the cylinder 49 through a pair of fluid connecting lines 51 and 52. The pilot valve 46 is shown in a null position wherein both of the fluid lines 51 and 52 are isolated from the supply line 47 and the piston 48 is motionless in the cylinder 49. The metering pin 23 is mounted directly to the actuating piston, so that the position of the piston 48 in the cylinder 49 determines the position of the metering pin or valve 23 in the nozzle 19. The position of the metering pin is fed back to one end of the pilot valve 46 by a tension spring 53 connected to a flange 54 on the metering pin or valve 23.

The entire control system is regulated to maintain the actuating piston 48 in a stationary position so long as the signal from the detector 32 is at the predetermined level. In this normal condition of the control system, shown in the drawing, the pilot valve 46 is in the null position. A force balance is maintained among the tension in the spring 53, the compression in a pilot valve spring 56 and the pressure on the diaphragm 45. Thus, as long as neither the flow rate nor the height of molten metal in the groove 12 varies, the fluid lines 51 and 52 are isolated from the supply line 47 and the metering pin 23 remains at the same setting. Therefore, the flow rate and metal height tend to remain constant.

Assume, next, that the flow rate of the molten metal through the entrance zone 39 begins to vary. For example, the rate of flow starts to decrease due to increased viscosity or decreased level of the metal in the tundish 17. The change is immediately reflected in an increased level of gamma radiation transmitted through the V-shaped detection zone (FIG. 2) constituting the gap or field of operation between the source 31 and the detector 32, since a lesser amount of molten metal is present in the entrance zone 39 to inhibit radiation transmittal. Any sudden change in the level of molten metal in groove 12 is also sensed by the differentiating circuit 61.

Due to the increase in the total gamma radiation transmitted through the V-shaped detecting zone, the count rate increases and the voltage of the signal applied to the controller 42 increases. The controller acts to decrease the pressure in the fluid line 44 to the diaphragm 45 so as to reposition the pilot valve 46 downwardly from the depicted null position. A new force balance is achieved among the springs 53 and 56 and the diaphragm 45. Pressurized fluid from the supply line 47 is meanwhile applied through the fluid line 52 to move the actuating piston 48 so as to withdraw the metering pin 23 away from the opening in the nozzle 19. The repositioning of the metering pin 23 is fed back to the pilot valve 46 by a reduction in the tension of spring 53 acting to deflect the diaphgram 45. This alters the force balance once more, tending to return the diphragm and the pilot valve to the null position. Simultaneously, the piston 48 and the metering pin 23 are maintained in the new position and the flow of molten metal through the nozzle 19 tends to return to the predetermined flow rate due to the increase in the flow area through the nozzle provided by the repositioning of the metering pin. Repetitively controlled corrections return the flow rate to the predetermined valve, the pilot valve 46 to the null position, and the total radiation detected to the predetermined amount of radiation.

The controller 42 is set or adjusted so as to be preferably operative to momentarily provide an initial pressure decrease of a magnitude greater than that proportional to the increase in the voltage signal for large deviations thereof from a predetermined value. Such momentary over-compensation in the pressure signal, occurring when the flow rate deviation is of large magnitude, acts to restore a depletion in the level of the molten metal in the casting wheel groove 12 which has been caused by the momentary decrease of large magnitude in the flow rate prior to correction. The large deviation in the flow rate thereafter is eliminated by action of the control system to reposition the metering pin 23 at a proportionally compensated flow regulating setting. The control system is repetitively operated by the cyc ic return of the pilot valve 46 to the null position. This cyclic operation of the pilot valve continues until the total detected radiation is restored to the predetermined value. Through the operation of the control system, the predetermined flow rate and level are restored.

Similarly, should the flow rate begin to increase due, for example, to an increased level or a decreased viscosity of the metal in the tundish 17, the control system would act to restore the flow rate to the predetermined condition thereof. A decreased gamma radiation total is sensed by the detector 32 and the control system acts to reposition the pilot valve 46 upwardly from the depicted position to apply pressurized fluid from the supply line 47 to the fluid line 51. The metering pin 23 is moved further into the opening in the nozzle 19 by the actuating piston 48 to attain a new position and a new flow regulating setting. The new position assumed by the metering pin 23 in creases the tension in the spring 53 and this increased tension is fed-back through the spring 53 to return the diaphragm 45 and the pilot valve 46 to the null position. With the new setting of the metering pin, the predetermined flow rate, thus, is restored. If the predetermined total of radiation is not detected, the control system will continue to operate until such time as the predetermined radiation is detected. Meanwhile, any momentary increase in the level of the molten metal in the casting groove 12, caused by a momentary flow increase of large magnitude, will be compensated by an initial and momentary overcorrecting movement of the pressure-operated actuating piston 48 into the nozzle 19.

The flow rate control system forming a part of the invention, thus, is repetitively operated and functions in response both to the rate of change of molten metal flow through the entrance zone 39 and to changes in the level of molten metal in the casting wheel groove 12, acting to restore both of these factors to predetermined values. The ability of the system to act in response to changes in the flow rate provides more rapid and more exact con trol than would a system responsive solely to changes of the level of molten metal in the groove 12.

It is to be understood that the above-described apparatus is simply illustrative of one embodiment of the invention. Many modifications may be made without departing from the invention.

What is claimed is:

1. In a continuous casting apparatus, a control system for maintaining a substantially constant flow rate in molten metal flowing out from a tundish through an exit orifice and then passing through an entrance zone into a peripheral groove in a rotating wheel partially enclosed by a traveling band, which control system comprises:

a nozzle surrounding said exit orifice to direct the flow of molten metal through the entrance zone and toward a metal receiving portion of the groove enclosed by the band;

means cooperating with the nozzle for metering the flow of molten metal into the entrance zone;

a first linearly extending gamma radiation emitting element positioned at one side of the wheel with a downstream end of the first element disposed adjacent to the metal receiving portion of the groove and with an upstream end of the first element extending along the entrance zone and generally toward the nozzle;

a second linearly extending gamma radiation emitting element positioned at said one side of the wheel with an upstream end of the second element disposed 8 adjacent to the metal receiving portion of the groove and with a downstream end of the second element extending chordally along the groove so as generally to follow the curvature of the groove;

detector means positioned at the other side of the wheel from said one side and coextensive with said first and second elements for measuring gamma radiation transmitted from said first and second elements through both the entrance zone and a portion of the groove below the metal receiving portion; and

means responsive to the quantity of transmitted gamma radiation measured by said detector means for selectively positioning the metering means to maintain the flow rate substantially constant.

2. In a continuous casting apparatus:

a source of gamma radiation;

means spaced from said source to define a generally V-shaped zone for detecting the level of gamma radiation received from the source;

a rotating casting wheel having a casting groove therein and positioned so that a portion of the groove is located in said zone between the source of gamma radiation and the detecting means;

a tundish having a bottom orifice for flowing out molten metal;

a nozzle extending from said orifice to direct flowing molten metal into said zone between the source and the detecting means and then into said portion of the groove in the zone;

a selectively positionable, tapered flow metering pin projecting through the orifice and into the nozzle to control flow of molten metal into the groove;

means responsive to the total gamma radiation detected by said detecting means varying from a predetermined value for generating a correction signal having a voltage proportional to the variation of the detected radiation from the predetermined value;

a source of pressurized fluid;

means operable by fluid pressure for selectively positioning said flow metering pin;

pilot valve means interconnected between said source of pressurized fluid and said fluid pressure operable positioning means and responsive to the voltage of the generated correction signal for selectively applying pressurized fluid to said fluid pressure operable positioning means so as to selectively position the flow metering pin to control the flow of molten metal into the groove in the rotating casting wheel; and

feedback means including a spring connecting the pilot valve means with the flow metering pin and responsive to movement of the flow metering pin for moving the pilot valve means.

3. Ina system for controlling the flow of molten metal into a circumferential groove formed in a constantly rotating wheel having a band spanning a portion of the circumferential groove to define a casting chamber between the wheel and the band, said band mounted for rotation with the wheel and initially engaging the wheel at a molten metal receiving mouth and leaving the wheel at a cast metal withdrawing exit wherein the improvement comprises:

a tundish forreceiving a supply of molten metal;

a spout running from the underside of the tundish and projecting into a gap formed by the advancing belt and the wheel for flowing molten metal into said mouth;

a valve projecting into the spout for metering the flow of metal; 7

means for moving the valve to vary the amount of metal flowing from the spout into said mouth;

means for rotating the wheel at a speed sufiicient to advance cast metal through said exit to consume the metal flowing into said mouth and maintain substantially constant the surface level of the molten metal in the mouth;

radiation for operating said valve moving means to regulate the total amount of metal flowing into said mouth and the level of molten metal in said mouth. 4. In a system for controlling the flow of molten metal as set forth in claim 3, wherein:

the valve includes a tapered flow metering pin projecting into said spout, the valve moving means includes;

a piston mounted on one end of said pin,

a cylinder surrounding said piston and mounting the piston for reciprocation therein,

a pair of fluid lines, each connected to a diiferent end of the cylinder at a different side of the piston,

a source of pressurized fluid,

pilot valve means connected to said fluid lines for selectively apportioning pressure from said fluid pressure source between said fluid lines,

feedback means including a spring connecting said metering pin to the pilot valve means and responsive to movement of the metering pin for moving the pilot valve means,

and the valve operating means includes;

means responsive to measured changes in passed radiation for generating voltage signal varying with said changes, and

control means cooperating with said feedback means and responsive to said voltage signal for selectively positioning the pilot valve to regulate the position of the piston in the cylinder and the metering pin in the spout.

5. In a system for controlling the flow of molten metal as set forth in claim 3, said source of gamma radiation comprising:

a body of gamma radiation emitting material positioned proximate to an edge of the rotating Wheel at a location adjacent to the molten metal receiving mouth and configured to follow at least a portion of the curvature of the circumferential groove downstream of the mouth for measuring the surface level of the molten metal, while extending upstream generally toward the spout from the mouth for sampling the flow of molten metal into the mouth.

6. In a system for controlling the flow of molten metal as set forth in claim 5, said body of gamma radiation emitting material comprising a plurality of linearly extending gamma radiation emitting elements arrayed to follow generally the groove extending circumferentially about the wheel.

7. In a system for controlling the flow of molten metal as set forth in claim 6, said plurality of linearly extending gamma radiation emitting elements constituting two such elements positioned in partially overlapping relationship with a trailing end of one of the elements and a leading end of the other of the elements overlapped adjacent to a normal control level for the surface of molten metal within said molten metal receiving mouth.

References Cited UNITED STATES PATENTS 2,586,713 2/1953 Ratcliffe et a1 l64l55 3,080,627 3/1963 Hoteko l64278 X 3,300,820 1/1967 Tiskus et a1 l64l55 3,375,862 4/1968 Boitchenko et a1. 164-281 X FOREIGN PATENTS 1,373,146 4/1964 France.

I. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner US. Cl. X.R. 1644, 281

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,5 79 Dated September 15, 1970 Patent No.

Joseph I. Cole, William C. Martin, and Stephen F. Skala h is certified that error appears in the above-identified patent and that said Letters Patent are'hereby corrected as shown below:

Column 1, lines 5-8 should read:

Joseph I. Cole, Staten Island, N. Y., assignor to Nassau smelting 8c Refining C0,, Incorporated, Tottenville, Staten Island, N. Y., a corporation of New York, and William C. Martin, Naperville, and Stephen F. Skala,

Berwyn, 111. assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York.

Signed and sealed this 7th day of March 1 972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

